203. 移除链表元素https://leetcode-cn.com/problems/remove-linked-list-elements/
示例 1:
输入:head = [1,2,6,3,4,5,6], val = 6 输出:[1,2,3,4,5]
示例 2:
输入:head = [], val = 1 输出:[]
示例 3:
输入:head = [7,7,7,7], val = 7 输出:[]
提示:
- 列表中的节点数目在范围
[0, 104]
内 1 <= Node.val <= 50
0 <= val <= 50
解题思路:
- 小坑1,当链表为空不能删
- 小坑2,头部为删除值很难处理(最后再判断)
- 难点:定义两个指针,一个 cur (删除节点)在 head.next ,一个 prev (删除前驱)在 head 上,当cur在删除的值上时,令 prev.next=cur.next(删除元素),接着 cur=cur.next(向后走一步),若后面的值还是要删的,prev 不动,cur执行之前的操作,若不是,prev = cur (prev到cur位置),接着 cur.next(向后走一步),执行以上操作直到 cur.next 为 null 停止。
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
public class Solution {
public ListNode removeElements(ListNode head, int val) {
if(head==null){
return null;
}
ListNode prev = head;
ListNode cur = head.next;
while(cur !=null){
if(cur.val==val){
prev.next = cur.next;
cur = cur.next;
}else{
prev = cur;
cur = cur.next;
}
}
if(head.val == val){
head = head.next;
}
return head;
}
}